Method for preparing an amine hydrochloride suspension

ABSTRACT

The invention relates to a method for preparing a suspension of a hydrochloride of an organic amine, comprising the following steps of (i) initially charging at least one organic solvent in a reaction vessel to form a liquid level, (ii) adding hydrogen chloride, (iii) adding the organic amine, wherein the organic amine is added below the liquid level present in the reaction vessel and steps (ii) and (iii) are at least partly carried out simultaneously. Furthermore, the present invention also relates to a method wherein the suspension obtained after step (iii) is reacted in a step (iv) with phosgene to obtain the organic isocyanate corresponding to the organic amine used, to the corresponding organic isocyanate and to the use of the organic isocyanate for producing polyisocyanates.

CROSS REFERENCE TO RELATED APPLICATIONS

The present application claims priority under the Paris Convention to EPSerial No. 19179482, filed Jun. 11, 2019, the entire contents of whichare incorporated herein by reference.

FIELD OF THE INVENTION

The present invention relates to a method for preparing a suspension ofa hydrochloride of an organic amine, comprising the following steps of(i) initially charging at least one organic solvent in a reaction vesselwith formation of a liquid level, (ii) adding hydrogen chloride, (iii)adding the organic amine, wherein the organic amine is added below theliquid level present in the reaction vessel and steps (ii) and (iii) areat least partly carried out simultaneously. Furthermore, the presentinvention also relates to a method wherein the suspension obtained afterstep (iii) is reacted in a step (iv) with phosgene to obtain the organicisocyanate corresponding to the organic amine used, to the correspondingorganic isocyanate and to the use of this organic isocyanate forproducing polyisocyanates.

BACKGROUND OF THE INVENTION

It is known that organic isocyanates can be prepared by reactingphosgene with the corresponding amines. In particular in the case of theconversion of aliphatic amines to the corresponding aliphaticisocyanates, owing to the high reactivity, high contents of undesiredby-products continuously form, for example resinous, high-boilingcompounds or chlorinated compounds, which form by deamination.

There has therefore been no lack of attempts to avoid or at least reducethese problems. For instance, DE 1 593 588 describes the phosgenation ofxylylenediamine, in which hot phosgenation is operated with an excess ofphosgene at 120 to 180° C. and a pressure of 2 to 5 atü (196 to 490kPa). Also with this method, at most ca. 90% of the desired xylylenediioscyanate and correspondingly 10% and more of undesired by-productsare formed.

EP 1 908 749 describes a variant of the method in which the amine in theso-called base phosgenation is not reacted directly with phosgene.Rather the amine is firstly reacted with hydrogen chloride to thecorresponding amine hydrochloride which is then phosgenated. It shouldbe noted that using the method according to the prior art, particularlyat amine concentrations above 5% by weight in the solvent, very highlyviscous suspensions are obtained which have poor flowability and pumpingcapability and therefore also poor stirrability. The problem is solvedaccording to the document mentioned by operating the formation of thehydrochloride under a pressure which is at least 0.01 MPa aboveatmospheric pressure.

A disadvantage of such a method is operation under positive pressurewhich places increased requirements on the apparatus and, in the case ofexternal leakage, the risk potential increases due to leaking gaseoushazardous substances.

DE 69 011 358 also describes a method for preparing xylylenediisocyanate in which xylylenediamine hydrochloride is reacted withphosgene in the presence of an ester as reaction solvent. Thexylylenediamine in this case in one embodiment in a first step isconverted to the hydrochloride at a temperature of 30° C. or less withhydrogen chloride and later phosgenated at 120 to 170°. Owing to theexothermic reaction, strong cooling is required for this procedure inorder to minimize the formation of carboxamides by aminolysis of thesolvent. However, it cannot be completely prevented. On the other hand,it is recommended not to lower the temperature below 0° C. such thatultimately only a narrow process window remains. Furthermore, thismethod is limited to the use of esters as reaction solvent wherein thepreviously mentioned aminolysis of the solvent occurs as a sidereaction. In a phosgenation commonly preferred chlorinated aromaticsolvents such as chlorobenzene or ortho-dichlorobenene which, owing totheir physical and chemical properties, are particularly suitable forthe preparation of isocyanates by phosgenation of the correspondingamines, cannot be used in this method.

DETAILED DESCRIPTION OF THE INVENTION

Proceeding from this prior art, the object of the present invention wasto avoid the known disadvantages of the prior art, the object of thepresent invention particularly being to obtain even at standard pressureor in an unpressurized process and at temperatures above 30° C., astirrable and pumpable suspension comprising the respectivehydrochloride of organic amines. A further object of the invention wasthe economic, efficient and simple preparation of aliphatic isocyanates,preferably aliphatic diisocyanates, by phosgenation of appropriatelyprepared amine hydrochlorides which are in suspension.

This object was solved according to the invention by the method forpreparing a suspension of a hydrochloride of an organic amine comprisingthe following steps:

-   -   (i) initially charging at least one organic solvent in a        reaction vessel with formation of a liquid level,    -   (ii) adding the organic amine,    -   (iii) adding hydrogen chloride,    -   wherein the organic amine is added below the liquid level        present in the reaction vessel and steps (ii) and (iii) are at        least partly carried out simultaneously.

The individual steps of the method according to the invention aredescribed in detail below.

Step (i) of the method according to the invention comprises initiallycharging at least one organic solvent in a reaction vessel to form aliquid level.

In the context of the present invention, all organic solvents thatappear suitable to a person skilled in the art for preparinghydrochlorides of organic amines can generally be used.

In accordance with the invention, an aprotic solvent is preferably used.Particularly preferably, the at least one organic solvent is selectedfrom the group consisting of aromatic hydrocarbons, halogenated aromatichydrocarbons, particularly chlorinated aromatic hydrocarbons, esters,ethers, halogenated hydrocarbons and mixtures thereof.

A particularly preferred aromatic hydrocarbon used in accordance withthe invention is toluene.

Particularly preferred halogenated hydrocarbons used in accordance withthe invention are selected from the group consisting of bromobenzene,chlorobenzene, dichlorobenzene, for example ortho-dichlorobenzene, andmixtures thereof.

The organic solvents used in accordance with the invention are veryparticularly preferably chlorobenzene, dichlorobenzene, for exampleortho-dichlorbenzene, or mixtures thereof.

The method according to the invention can generally be carried out inany reactor deemed as suitable to a person skilled in the art. By meansof steps (ii) and (iii), sufficient mixing can take place. It is evidentto a person skilled in the art that the use of an additional mixingdevice is not essential but is an advantageous configuration.

For example, a stirred vessel is suitable as reactor. A suitable stirredvessel is described, for example, in DE 19957816 A1. It is preferably arotationally symmetric stirred vessel with a vertical main axis. Thestirred vessel can have different diameters along this main axis but ispreferably essentially cylindrical. The base and top can be constructed,for example, with a dish-shaped or flat end. For temperature control,the stirred vessel can be provided with heat exchanger pipes, welded-onhalf-tube profiles, a double-jacketed and/or a pillow-plate system knownto those skilled in the art or heat exchanger plate system, wherein theheat exchanger pipes can be configured either internally or externally.

Inlet and outlet nozzles can be positioned at any point on the wall, topand bottom of the stirred vessel. In order to fulfil the essentialfeature of the invention that the organic amine is added below theliquid level present in the reaction vessel, it is preferred inaccordance with the invention that at least one first feed line for theorganic amine or the solution of the organic amine is configured suchthat it flows into the reactor in the lower region. This can beachieved, for example, by means of a nozzle in the lower region of thereactor which may optionally be provided with a jet nozzle through whichthe organic amine or the solution of the amine can be injected into thereaction mixture. By means of the addition of the organic amine or thesolution of the amine mentioned above, especially by injection,sufficient mixing of the suspension can for example already be achieved.Alternatively or in addition other mixing devices can also be used.Suitable mixing devices are, for example, stirrers, jet nozzles orultrasound mixers. Preference is given to using a stirrer mounted on arotating shaft. When using jet nozzles it is conceivable, for example,to withdraw part of the reaction mixture and feed it again to thereaction vessel through the jet nozzle or to add the amine or the aminesolution through such a jet nozzle such that there will automatically bemixing of the reaction mixture.

In a preferred embodiment is a method for preparing a suspension of ahydrochloride of an organic amine comprising the following steps:

-   -   (i) initially charging at least one organic solvent in a        reaction vessel to form a liquid level,    -   (ii) adding the organic amine,    -   (iii) adding hydrogen chloride,    -   wherein the organic amine is added below the liquid level        present in the reaction vessel and steps (ii) and (iii) are at        least partly carried out simultaneously and the resulting        suspension is intermixed during the amine addition.

All other embodiments in the description and the patent claims can becombined with one another as desired and in particular with theaforementioned embodiment, unless the context clearly indicatesotherwise.

In a preferred embodiment, the feed line flows into the reactor via adip tube such that when carrying out the method according to theinvention, the organic amine or the solution of the organic amine ispassed through the dip tube directly into the reaction mixture.

The present invention therefore relates preferably to the methodaccording to the invention wherein step (iii) is effected using a diptube.

The ratio of the fill height to the diameter of the stirred vessel inaccordance with the invention is preferably from 0.5:1 to 1.5:1. Higherratios are also possible but generally also require the use ofmulti-stage mixing devices, preferably multi-stage stirring elements. Itshould be noted that by adding the reactants in the course of themethod, the fill height in the vessel changes. Particularly preferably,although not mandatory, the process parameters such as initial filllevel, vessel size and metering amounts are selected such that the ratioof fill height and diameter of the stirred vessel is always in the rangespecified above. If by the addition of the amine the range specified isbreached, it is advantageous to use a multi-stage mixing device,preferably a multi-stage mixing element, such that the entire reactionmixture is well-dispersed at all times.

It is generally advantageous if the fill height of the solvent initiallycharged is so high that the mixing device, preferably the mixingelement, is immersed in the liquid such that from the start good mixingand the highest possible heat transfer can be provided.

In accordance with the invention, the hydrogen chloride used ispreferably hydrogen chloride gas. In addition, the reactor is thereforepreferably provided with a second feed line for hydrogen chloride gas.Various embodiments are available for the gas feed line. If the hydrogenchloride gas is passed over, i.e. above the liquid level in the reactor,it is preferable in accordance with the invention to use aself-aspirating aeration stirrer. More preferably, the addition takesplace via a nozzle in the lower region of the reactor, i.e. below theliquid level. The addition is particularly preferably via an inlet pipewhich flows into the reactor below the stirrer, preferably in a gasdiffuser, via which the gas already diffused as much as possible isintroduced into the liquid below the stirrer. Also in this case,particular preference is given to using a self-aspirating aerationstirrer such that optimal dispersion of the hydrogen chloride gasintroduced results from the external addition below the stirrer and thediffusion of the aspirated gas again from the gas space above theliquid. In a further preferred embodiment of the method according to theinvention, an aeration stirrer with a hollow shaft is used forintroducing the hydrogen chloride gas, wherein preferably compressed gasis fed to the hollow shaft via the second feed line.

Self-aspirating aeration stirrers in accordance with the invention areunderstood to mean those stirrers which are driven by a hollow shaftwhich have openings in the upper region, i.e. above the liquid level inthe reactor, through which gas is aspirated from the gas space into thehollow shaft. The aspirated gas is transported downwards through thehollow cavity and escapes again through further openings in the stirrerblade elements below the liquid surface where it is mixed intensivelywith the liquid.

For addition of the organic solvent, either the first feed line can beused or alternatively a further, third, feed line. Other nozzles can beused for process monitoring, for example by means of sensors, sightglasses or sampling devices.

In addition, the reactor used in accordance with the invention ispreferably equipped with a suitable stirrer, for example an aerationstirrer, paddle stirrer and/or a dynamic mixer selected from the groupconsisting of disperser disks, rotor-stator systems and combinationsthereof.

The present invention therefore preferably relates to the methodaccording to the invention, wherein steps (ii) and (iii) are carried outwhile stirring with the aid of an aeration stirrer, a paddle stirrer ora dynamic mixer selected from the group consisting of disperser disks,rotor-stator systems and combinations thereof.

The reactor preferably used in accordance with the invention furthermorealso has at least one offgas line. Appropriate suitable offgas lines areknown per se to those skilled in the art.

The organic solvent which is filled into the reactor in step (i)according to the invention may in this case already contain certainconcentrations of the organic amine to be reacted. This concentrationis, for example, 5% by weight or less, preferably 3% by weight or less,particularly preferably 2% by weight or less. If the organic amine isalready present dissolved in the solvent, it is preferably present in anamount of at least 0.001% by weight. The organic amine can in accordancewith the invention already be dissolved beforehand in the solvent.Alternatively, the solution is prepared only in the reaction vessel.

Particularly preferably however, the at least one organic solvent, wheninitially charging in the reactor, is initially free of organic amine tobe reacted except for possible traces that may occur.

In the method according to the invention, the temperature of the organicsolvent in the reaction vessel prior to step (ii) is preferably adjustedto −20 to 100° C., particularly preferably 20 to 90° C., especiallypreferably 30 to 90° C.

Step (ii) of the method according to the invention comprises theaddition of hydrogen chloride.

Hydrogen chloride (HCl) is known per se to those skilled in the art andcan be added in accordance with the invention as a gas or in aqueoussolution as hydrochloric acid. In accordance with the invention,hydrogen chloride is preferably added as a gas, optionally in mixtureswith one or more further gases, for example inert gases such as nitrogenor noble gases, preferably nitrogen. In the case that hydrogen chlorideis added in a mixture with one or more inert gases, the content ofhydrogen chloride in the gas mixture is preferably 5 to 99% by weight,particularly preferably 50 to 99% by weight, especially preferably 80 to99% by weight.

Methods for preparing hydrogen chloride are known per se to thoseskilled in the art, for example it can be produced from the elements ina chlorine detonating gas reaction or is obtained as by-product in thechlorination of organic compounds.

Hydrogen chloride is added in gaseous form in accordance with theinvention preferably at a temperature of −20° C. to 100° C.,particularly preferably 10° C. to 50° C.

In the possible case according to the invention that organic amine isalready in the reaction vessel, it is advantageous to initially meter inhydrogen chloride in an amount that is sufficient to fully convert theorganic amine initially charged to the corresponding hydrochloride,before starting metering in further organic amine according to step(iii).

It is also possible in accordance with the invention to begin themetering in of the hydrogen chloride at the same time as metering in theorganic amine (step (iii)). Owing to the higher risk of agglomerateformation in this embodiment, either the hydrogen chloride gas can bemetered in in accordance with the invention in higher excess based onthe amine, or after addition of the amine is complete further hydrogenchloride is added until the total amount of organic amine has beenconverted to the hydrochloride. In this case, a higher excess preferablysignifies an equivalence ratio of HCl to amine of from 1.1:1 to 20,particularly preferably from 1.2:1 to 5:1.

The hydrogen chloride gas is preferably introduced below the liquidlevel in the reactor. The hydrogen chloride gas is particularlypreferably introduced below the mixing device, preferably the mixingelement, especially preferably the addition being carried out through agas diffuser below the mixing device, preferably the mixing element.

The gas feed device is preferably positioned such that, even in the caseof thrombus formation, the feed always takes place in the liquid and notin the gas space.

Step (iii) of the method according to the invention comprises theaddition of the organic amine.

The organic amines used can in principle be all compounds having primaryamino groups known to those skilled in the art. However, in accordancewith the invention, preference is given to those compounds having atleast 2, particularly preferably 2 or 3 NH₂ groups which may be bondedaliphatically, cyclopaliphatically, araliphatically or aromatically. Inaccordance with the invention, very particular preference is given tothose amines having 2 aliphatically, cycloaliphatically and/oraraliphatically bonded NH₂ groups.

Suitable aromatic amines are, for example, selected from the groupconsisting of pure isomers or isomeric mixtures of diaminotoluene,diaminodimethylbenzene, diaminonaphthalene, diaminobenzene,diaminodiphenylmethane and mixtures thereof. Particularly preferredaromatic amines are selected from the group consisting of2,4-diaminotoluene, 2,6-diaminotoluene, 1,5-diaminonaphthalene,p-phenylenediamine and mixtures thereof.

Suitable aliphatic, cycloaliphatic or araliphatic amines are, forexample, selected from the group consisting of 1,4-diaminobutane,1,5-diaminopentane (PDA), 1,6-diaminohexane (HDA), 1,11-diaminoundecane,1-amino-3,5,5-trimethyl-5-aminomethylcyclohexane (IPDA),bis(p-aminocyclohexyl)methane (PACM), 1,5-diamino-2-methylpentane,2,5-diamino-2,5-dimethylhexane, 1,4-diaminocyclohexane,2,4-hexahydrotoluylenediamine, 2,6-hexahydrotoluylenediamine (H6TDA),1,3-bis(aminomethyl)benzene (m-XDA), 1,4-bis(aminomethyl)benzene(p-XDA), isomers of bis(aminomethyl)cyclohexane (H6-XDA),tetramethylxylylenediamine (TMXDA), isomeren ofbis(aminomethyl)norbornane (NBDA), neopentanediamine,2,4,4-trimethylhexamethylenediamine, 2,2,4-trimethylhexamethylenediamineand mixtures thereof.

The present invention therefore preferably relates to the methodaccording to the invention, wherein the organic amine is selected fromthe group consisting of aromatic amines, preferably selected from thegroup consisting of pure isomers or isomeric mixtures of diaminotoluene,diaminodimethylbenzene, diaminonaphthalene, diaminobenzene,diaminodiphenylmethane and mixtures thereof, aliphatic, cycloaliphaticor araliphatic amines, preferably selected from the group consisting of1,4-diaminobutane, 1,5-diaminopentane (PDA), 1,6-diaminohexane (HDA),1,11-diaminoundecane, 1-amino-3,5,5-trimethyl-5-aminomethylcyclohexane(IPDA), bis(p-aminocyclohexyl)methane (PACM),1,5-diamino-2-methylpentane, 2,5-diamino-2,5-dimethylhexane,1,4-diaminocyclohexane, 2,4-hexahydrotoluylenediamine,2,6-hexahydrotoluylenediamine (H6TDA), 1,3-bis(aminomethyl)benzene(m-XDA), 1,4-bis(aminomethyl)benzene (p-XDA), isomers ofbis(aminomethyl)cyclohexane (H6-XDA), tetramethylxylylenediamine(TMXDA), isomers of bis(aminomethyl)norbornane (NBDA),neopentanediamine, 2,4,4-trimethylhexamethylenediamine,2,2,4-trimethylhexamethylenediamine and mixtures thereof.

In accordance with the invention, especially preferred organic aminesare selected from the group consisting of 1,5-diaminopentane (PDA),1,6-diaminohexane (HDA),1-amino-3,5,5-trimethyl-5-aminomethylcyclohexane (IPDA),1,3-bis(aminomethyl)benzene (m-XDA), isomers ofbis(aminomethyl)cyclohexane (H6-XDA), isomers ofbis(aminomethyl)norbornane (NBDA), 2,4,4-trimethylhexamethylenediamine,2,2,4-trimethylhexamethylenediamine and mixtures thereof.

In step (iii) of the method according to the invention, the organicamine or the mixture comprising more than one organic amine can be addedwithout solvent or dissolved in at least one solvent. Suitable solventsare all solvents known per se to those skilled in the art which areinert to the prevailing reaction conditions. The at least one organicamine is preferably dissolved in the same solvent or solvent mixturewhich is initially charged in the reactor. Particularly preferredsolvents to dissolve the at least one organic amine are thereforeselected from the group consisting of aromatic hydrocarbons, halogenatedaromatic hydrocarbons, particularly chlorinated aromatic hydrocarbons,esters, ethers and halogenated hydrocarbons and mixtures thereof.Particularly preferred aromatic hydrocarbons used in accordance with theinvention are selected from the group consisting of toluene,bromobenzene, chlorobenzene, dichlorobenzene, for exampleortho-dichlorobenzene, and mixtures thereof. In accordance with theinvention, particular preference is given to using chlorobenzene,dichlorobenzene or mixtures thereof.

In accordance with the present method, the organic amine is preferablyused dissolved in at least one solvent, preferably selected from thegroup consisting of aromatic hydrocarbons, halogenated aromatichydrocarbons, particularly chlorinated aromatic hydrocarbons, esters,ethers and halogenated hydrocarbons and mixtures thereof, especiallyselected from the group consisting of toluene, bromobenzene,chlorobenzene, dichlorobenzene, for example ortho-dichlorobenzene, andmixtures thereof.

The organic amine is preferably added as a solution in an inert solvent.The concentration of the organic amine in the solvent is preferably 5 to50% by weight, particularly preferably 10 to 30% by weight, based ineach case on the solution. In this manner, in accordance with theinvention, the formation of agglomerates due to local superelevatedconcentrations of the organic amine can be further minimized.

A feature essential to the invention is that the organic amine is addedbelow the liquid level present in the reaction vessel, wherein the inputis preferably effected via a dip tube. In accordance with the invention,below the liquid level present in the reaction vessel signifies thatpreferably the feed is effected continuously into the reaction mixturein the reaction vessel.

A further feature essential to the invention is that steps (ii) and(iii) are at least partly, preferably completely, carried outsimultaneously. In the context of the present invention, at least partlysignifies that the addition is effected simultaneously preferably to anextent of 40 to 100%, particularly preferably 80 to 99%, particularlypreferably 80 to 95%. That means that this mass fraction of the totalamount of the organic amine to be added is is passed into the reactorwhile also hydrogen chloride is passed into the reactor in order toreact with the organic amine to the corresponding hydrochloride.However, it is also possible in accordance with the invention thatorganic amine or hydrogen chloride are partly initially charged and thenthe simultaneous addition is carried out.

The metering in of the organic amine and hydrogen chloride is carriedout in a preferred embodiment of the method according to the inventionsuch that the hydrogen chloride is added in stoichiometric excess basedon the amino groups of the organic amine metered in. In this manner, itis prevented that the organic amine accumulates to undesired highconcentrations and a finely divided suspension is obtained.

While both reactants are metered in, the substance streams of hydrogenchloride and organic amine are preferably at an equivalence ratio toeach other of from 1:1 to 10:1, particularly preferably 1:1 to 3:1,especially preferably 1.05:1 to 1.8:1.

The total amount of hydrogen chloride metered in is preferablysufficient to fully convert the organic amine, i.e. to an extent of morethan 99%, preferably more than 99.5% and particularly preferably morethan 99.9% to the hydrochloride.

The end concentration of hydrochloride in the reaction mixture ispreferably 5 to 30% by weight, particularly preferably 7 to 25% byweight, especially preferably 10 to 20% by weight. The value for the endconcentration of hydrochloride is calculated from the mass of theorganic amine present in the reactor under consideration of themolecular weight increase due to formation of the hydrochloride, whereina complete conversion of all amino groups to the corresponding ammoniumchloride groups is assumed, based on the total mass of the reactorcontent. In the preferred concentration range specified in accordancewith the invention, a particularly advantageous compromise of highefficiency of the method and good handling of the suspension isavailable.

After the preparation of the hydrochloride according to the inventioncomprising steps (i), (ii) and (iii), the suspension obtained after step(iii) is preferably reacted in a step (iv) with phosgene to obtain theorganic isocyanate corresponding to the organic amine used.

The present invention therefore preferably relates to the methodaccording to the invention wherein the suspension obtained after step(iii) is reacted in a step (iv) with phosgene to obtain the organicisocyanate corresponding to the organic amine used.

The suspension of hydrochloride obtained by the method according to theinvention can be subsequently converted to the corresponding isocyanateby reaction with phosgene. For this purpose, the suspension can eitherremain in the reaction vessel or be transferred to another reactionvessel.

For the phosgenation step, the same types of reaction vessels can beused as previously described for the preparation of the hydrochloridesuspension. The suspension is then heated to a temperature of 120 to200° C. with introduction of phosgene, optionally diluted with an inertgas or gas mixture, for example nitrogen or noble gases. Particularlyfor less thermally stable isocyanates, it is preferable that thistemperature is 120 to 170° C., particularly preferably 120 to 160° C.

In accordance with the invention therefore, the phosgenation ispreferably carried out at a temperature of 120 to 170° C., particularlypreferably 130 to 160° C. The phosgenation can be carried out either atatmospheric pressure or at positive pressure. The pressure is preferably1 to 10 bar(a), particularly preferably 1 to 5 bar(a).

Phosgene is preferably used in stoichiometric excess for thephosgenation. Higher excesses act positively on the reaction rate andtherefore the duration of the reaction but naturally impair the economyof the method. Typically therefore the reaction is carried out using aphosgene excess of 100 to 500%, preferably 150 to 300%. Optionally, aninert gas can also be introduced into the reaction mixture.

The phosgene is added to the hydrochloride suspension, preferably byintroducing gaseous phosgene. The phosgene is preferably introducedbelow the liquid level in the reactor. The phosgene is particularlypreferably introduced below the mixing device, especially preferably theaddition being carried out through a gas diffuser below the mixingdevice. Aeration stirrers with hollow shaft are preferably used asmixing device as already described above.

In an alternative embodiment, the phosgene is introduced into thereactor as a solution in an inert solvent. The same solvent ispreferably used for this purpose in which the suspension of thehydrochloride is also present.

In a further alternative embodiment, it is also possible to initiallycharge a phosgene solution in a reaction vessel and to add thehydrochloride suspension prepared according to the invention to thissolution.

It can be advantageous to flush the feed lines for amine and/or hydrogenchloride, before and/or after the reaction, with solvent and/or inertgas, preferably nitrogen.

After completion of the reaction, i.e. at largely complete conversion,i.e. preferably 80 to 99%, particularly preferably 90 to 99% of thetheoretical value, of the hydrochloride to the corresponding isocyanate,excess phosgene and hydrogen chloride are preferably removed from thereaction mixture. For this purpose, generally an inert gas, preferablynitrogen, is passed through the reaction mixture. Optionally, phosgeneand hydrogen chloride can be removed or be assisted also by applying anegative pressure. If needed, filtration can be carried out in order toremove solids possibly present such as unreacted hydrochlorideparticles.

Subsequently, the reaction product is preferably processed according tomethods known from the prior art, i.e. it is preferably purified in amulti-stage vacuum distillation. In particular, in this distillativeprocessing, the isocyanate is freed from solvent, chlorinatedby-products and higher-boiling residues.

Since solvents are preferably used for preparing isocyanates which havea lower boiling point than the respective isocyanate, the distillationpreferably comprises solvent removal. In this distillation step,low-boiling secondary components, particularly chlorinated low-boilingsecondary components, are removed. The solvent can, optionally afterfurther purification steps, be fed back again into the process.

In addition, such a purification process preferably comprises apurification by distillation to separate the isocyanate fromhigh-boiling residue. All distillation steps are preferably carried outunder reduced pressure in order to reduce the temperatures required fordistillation and thus the thermal stress on the product. In particular,this distillation step is carried out at a pressure of 5 to 50 mbar(a)and a bottom temperature of 90 to 250° C., preferably 120 to 170° C.When necessary, in order to suppress the formation of uretdiones in thedistillate, the distillate is preferably cooled as rapidly as possibleto temperatures below 90° C., preferably below 80° C. This can beachieved, for example, by quenching the distillate, especially by mixingwith product already cooled.

After step (iv) of the method according to the invention, the organicisocyanate is preferably obtained, in particular 1,5-diisocyanatopentane(PDI), 1,6-diisocyanatohexane (HDI),1-isocyanato-3,5,5-trimethyl-5-isocyanatomethylcyclohexane (IPDI),1,3-bis(isocyanatomethyl)benzene (m-XDI), isomers ofbis(isocyanatomethyl)cyclohexane (H6-XDI), isomers ofbis(isocyanatomethyl)norbornane (NBDI),2,4,4-trimethylhexamethylenediamine, 2,2,4-trimethylhexamethylenediamineor mixtures thereof, in pure form, i.e. at a purity of at least 99.5%.

The present invention also relates to an organic isocyanate obtainableby the method according to the invention. In particular, the presentinvention relates to an organic isocyanate obtainable by the methodaccording to the invention selected from the group consisting of1,5-diisocyanatopentane (PDI), 1,6-diisocyanatohexane (HDI),1-isocyanato-3,5,5-trimethyl-5-isocyanatomethylcyclohexane (IPDI),1,3-bis(isocyanatomethyl)benzene (m-XDI), isomers ofbis(isocyanatomethyl)cyclohexane (H6-XDI), isomers ofbis(isocyanatomethyl)norbornane (NBDI),2,4,4-trimethylhexamethylenediamine, 2,2,4-trimethylhexamethylenediamineand mixtures thereof.

The present invention also relates to the use of the organic isocyanatesaccording to the invention for producing polyisocyanates comprisingisocyanurate groups, polyisocyanates comprising uretdione groups,polyisocyanates comprising biuret groups, polyisocyanates comprisingurethane or allophanate groups, polyisocyanates comprisingoxadiazinetrione groups or iminooxadiazinedione groups and/oruretonimine-modified polyisocyanates.

Such polyisocyanates based on organic isocyanates according to theinvention or the organic isocyanate itself can be used, for example, forproducing plastics comprising urethane, thiourethane, isocyanurate,amide and/or urea groups by the polyisocyanate polyaddition process.Such polyisocyanate mixtures are particularly used for producinglight-stable polyurethane lacquers and coatings.

EXAMPLES Comparative Example 1

A stirred vessel composed of glass with a heat-controlled jacket and alength-to-internal diameter ratio of 1.2 was equipped with a paddlestirrer, where the stirrer paddle diameter to internal diameter of thereactor was at a ratio of 0.75. The stirred vessel was charged with 5 gof monochlorobenzene. At the same time 1 kg of m-xylylenediamine in 4 kgof o-dichlorobenzene was initially charged in a raw material reservoir.At the same time, with stirring at atmospheric pressure, hydrogenchloride gas was passed into the reactor via a gas inlet tube and theamine solution provided in the raw material reservoir was added, whereinthe amine solution was added from above, i.e. above the liquid level inthe stirred vessel. The metered addition was effected over 2 h at ametered addition rate of 321 g/h for hydrogen chloride and 2.5 kg/h forthe amine solution. The amine feed was then terminated and hydrogenchloride was further fed for 60 min at a metered addition rate of 150g/h. The temperature in the stirred vessel during the entire procedurewas maintained at 25° C. by means of the heat-controlled jacket.

Thick sticky deposits were evident on the wall of the stirred vessel, onthe stirrer and on the inlet nozzle of the amine solution. The reactionmixture obtained comprised large solid agglomerates with diameters >1mm, which settled out. The resulting reaction mixture was therefore nolonger suitable for being stirred or pumped.

Example 2 (According to the Invention)

The stirred vessel according to comparative example 1 was modified sothat now the amine solution was fed directly into the reaction mixturethrough a dip tube and therefore below the liquid level. In addition,after termination of the amine addition, hydrogen chloride was furtherfed for 30 minutes at a metered addition rate of 150 g/h. The experimentof comparative example 1 was repeated under otherwise unmodifiedconditions. The temperature in the stirred vessel was maintained at 25°C. by means of the heat-controlled jacket.

There were only minor deposits on the wall of the stirred vessel. Thestirrer and the dip tube for feeding were free of adhesions. Theresulting suspension could be stirred and pumped but still comprisedrelatively large solid particles but the size of which was below 1 mm indiameter.

Example 3 (According to the Invention)

For a further experiment, the stirred vessel was again modified byreplacing the paddle stirrer with an aeration stirrer. The experiment ofexample 2 (according to the invention) was repeated, wherein now thehydrogen chloride was introduced through the aeration stirrer. Inaddition, the reactor was preheated to 35° C. by the heat-controlledjacket and was maintained at this temperature during addition of thereactants. After completion of the experiment, only small deposits wereagain observed on the wall of the stirred vessel, while the stirrer andthe dip tube were free of deposits. The resulting suspension washomogeneous, finely-divided and could be stirred and pumped.

Example 4 (According to the Invention)

The experiment of example 3 (according to the invention) was repeated,wherein contrary to the conditions in example 3, the reactor waspreheated to 80° C. by the heat-controlled jacket and was maintained atthis temperature during the addition of the reactants. This againresulted in a homogeneous finely-divided, stirrable and pumpablesuspension and also deposits on the wall of the reactor could be furtherminimized.

Example 5 (According to the Invention)

The method was as in example 4 but an isomeric mixture of 2,2,4- and2,4,4-trimethylhexamethylenediamine was used as amine. This was placedin the raw material reservoir as a 20% by weight solution inmonochlorobenzene. The temperature was again regulated to 80° C. and themetered addition rate was 2.5 kg/h for the amine solution and 275 g/hfor hydrogen chloride. After 2 hours, the metered addition of amine wasterminated and hydrogen chloride was further fed for 30 min at a meteredaddition rate of 100 g/h. A homogeneous finely-divided, stirrable andpumpable suspension was again obtained. Deposits did not occur.

Comparative Example 6

In deviation from example 5, in comparative example 6 the reactor wasinitially charged with 10 kg of a 10% solution of the isomeric mixtureof 2,2,4- and 2,4,4-trimethylhexamethylenediamine in monochlorobenzeneand temperature-controlled at 25° C. Then, with vigorous stirring,hydrogen chloride gas was introduced over 2.5 h at a metered additionrate of 275 g/h. There were heavy deposits on walls and stirrers andrelatively large solid agglomerates with diameters >1 mm formed, whichsettled on the bottom of the vessel.

Example 7 (According to the Invention)

In the raw material reservoir, 900 g of isomeric mixture of 2,2,4- and2,4,4-trimethylhexamethylenediamine were initially charged in 4 kg ofmonochlorobenzene. In the stirred vessel, a further 100 g of the aminewere initially charged in 5 kg of monochlorobenzene. The reactionmixture was heated to 60° C. and while stirring initially 70 g ofhydrogen chloride were added through the aeration stirrer. Only then wasthe simultaneous metered addition of the amine solution and furtherhydrogen chloride begun. The metered addition rates were 2.45 kg/h forthe amine solution, which was fed in accordance with the inventionthrough a dip tube below the liquid level and 250 g/h for the hydrogenchloride. After 2 hours, the addition of amine was terminated andhydrogen chloride was further metered in for 30 min at a reduced meteredaddition rate of 100 g/h. After completion of the experiment, only smalldeposits were again observed on the wall of the stirred vessel, whilethe stirrer and the dip tube were free of deposits. The resultingsuspension was homogeneous, finely-divided and could be stirred andpumped.

Example 8 (According to the Invention)

In a stirred vessel modified as described in example 3, 5000 g ofmonochlorobenzene were initially charged and the reactor was preheatedto 70° C. by means of the heat-controlled jacket and maintained at thistemperature during addition of the reactants. A solution of 1000 g ofaniline in 4000 g of monochlorobenzene was added as amine solution fromthe raw material reservoir via the dip tube. Hydrogen chloride gas wasintroduced through the aeration stirrer. The metered addition rates were2 kg/h for the amine solution and 500 g/h for hydrogen chloride. After2.5 h all the amine had been added and further hydrogen chloride wasintroduced for 30 minutes at a metered addition rate of 100 g/h. Ahomogeneous finely-divided, stirrable and pumpable suspension wasobtained. Deposits did not occur.

Example 9 (According to the Invention)

The experiment of example 5 was repeated wherein, instead ofo-dichlorobenzene, in this case monochlorobenzene was initially chargedand the amine solution was added in o-dichlorobenzene. Other conditionsremained unchanged. A homogeneous finely-divided, stirrable and pumpablesuspension was again obtained. Deposits did not occur.

1. A method for preparing a suspension of a hydrochloride of an organicamine, comprising the following steps: (i) initially charging at leastone organic solvent in a reaction vessel to form a liquid level, (ii)adding hydrogen chloride, (iii) adding the organic amine, wherein theorganic amine is added below the liquid level present in the reactionvessel and steps (ii) and (iii) are at least partly carried outsimultaneously.
 2. The method according to claim 1, wherein thetemperature of the organic solvent in the reaction vessel prior to step(ii) is adjusted to −20 to 100° C.
 3. The method according to claim 1,wherein step (iii) is carried out using a dip tube.
 4. The methodaccording to claim 1, wherein the at least one organic solvent isselected from the group consisting of aromatic hydrocarbons, halogenatedaromatic hydrocarbons, particularly chlorinated aromatic hydrocarbons,esters, ethers, halogenated hydrocarbons and mixtures thereof.
 5. Themethod according to claim 1, wherein the organic amine is added as asolution in an inert solvent.
 6. The method according to claim 5,wherein the concentration of the organic amine in the solvent is 5 to50% by weight, based on weight of the solution.
 7. The method accordingto claim 1, wherein the substance streams of hydrogen chloride andorganic amine during steps (ii) and (iii) are in an equivalence ratio toeach other of from 1:1 to 10:1.
 8. The method according to claim 1,wherein the end concentration of hydrochloride in the reaction mixtureis 5 to 30% by weight.
 9. The method according to claim 1, wherein steps(ii) and (iii) are carried out while stirring with the aid of anaeration stirrer, paddle stirrer or a dynamic mixer selected from thegroup consisting of disperser disks, rotor-stator systems andcombinations thereof.
 10. The method according to claim 1, wherein theorganic amine is selected from the group consisting of aromatic amines.11. The method according to claim 1, wherein the suspension obtainedafter step (iii) is reacted in a step (iv) with phosgene to obtain theorganic isocyanate corresponding to the organic amine used.
 12. Theorganic isocyanate, obtainable by the method according to claim 11,selected from the group consisting of 1,5-diisocyanatopentane (PDI),1,6-diisocyanatohexane (HDI),1-isocyanato-3,5,5-trimethyl-5-isocyanatomethylcyclohexane (IPDI),1,3-bis(isocyanatomethyl)benzene (m-XDI), isomers ofbis(isocyanatomethyl)cyclohexane (H6-XDI), isomers ofbis(isocyanatomethyl)norbornane (NBDI),2,4,4-trimethylhexamethylenediamine, 2,2,4-trimethylhexamethylenediamineand mixtures thereof.
 13. In a process for producing polyisocyanatescomprising one of isocyanurate groups, polyisocyanates comprisinguretdione groups, polyisocyanates comprising biuret groups,polyisocyanates comprising urethane or allophanate groups,polyisocyanates comprising oxadiazinetrione groups oriminooxadiazinedione groups and/or uretonimine-modified polyisocyanates,the improvement comprising including the organic isocyanate according toclaim
 12. 14. One of polyisocyanates comprising isocyanurate groups,polyisocyanates comprising uretdione groups, polyisocyanates comprisingbiuret groups, polyisocyanates comprising urethane or allophanategroups, polyisocyanates comprising oxadiazinetrione groups oriminooxadiazinedione groups and/or uretonimine-modified polyisocyanatesproduced by the process according to claim
 13. 15. In a process forproducing plastics comprising urethane, thiourethane, isocyanurate,amide and/or urea groups by the polyisocyanate polyaddition process orfor producing light-stable polyurethane lacquers and coatings, theimprovement comprising including the organic isocyanate according toclaim
 12. 16. method according to claim 10, wherein the organic amine isselected from the group consisting of pure isomers or isomeric mixturesof diaminotoluene, diaminodimethylbenzene, diaminonaphthalene,diaminobenzene, diaminodiphenylmethane and mixtures thereof.
 17. Themethod according to claim 10, wherein the organic amine an aliphatic,cycloaliphatic or araliphatic amine selected from the group consistingof 1,4-diaminobutane, 1,5-diaminopentane (PDA), 1,6-diaminohexane (HDA),1,11-diaminoundecane, 1-amino-3,5,5-trimethyl-5-aminomethylcyclohexane(IPDA), bis(p-aminocyclohexyl)methane (PACM), 1,5-diamino-2-methylpentane, 2,5-diamino-2,5-dimethylhexane,1,4-diaminocyclohexane, 2,4-hexahydrotoluylenediamine,2,6-hexahydrotoluylenediamine (H6TDA), 1,3-bis(aminomethyl)benzene(m-XDA), 1,4-bis(aminomethyl)benzene (p-XDA), isomers ofbis(aminomethyl)cyclohexane (H6-XDA), tetramethylxylylenediamine(TMXDA), isomers of bis(aminomethyl)norbornane (NBDA),neopentanediamine, 2,4,4-trimethylhexamethylenediamine,2,2,4-trimethylhexamethylenediamine and mixtures thereof